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lyzzy7

  • 3 years ago

multiple choice question! please help! Suppose y varies directly with x, and y = 14 when x = –4. What is the value of y when x = –6? –21 10 18 21

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  1. jim_thompson5910
    • 3 years ago
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    y varies directly with x means that y = kx

  2. jim_thompson5910
    • 3 years ago
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    when x = -4, y is y = 14 so y = kx turns into 14 = k*(-4)

  3. jim_thompson5910
    • 3 years ago
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    solve for k and tell me what you get

  4. lyzzy7
    • 3 years ago
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    -3.5, But I think Im wrong..

  5. jim_thompson5910
    • 3 years ago
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    you're correct

  6. jim_thompson5910
    • 3 years ago
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    so y = kx turns into y = -3.5x

  7. jim_thompson5910
    • 3 years ago
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    now they want to know the value of y when x = -6

  8. jim_thompson5910
    • 3 years ago
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    so y = -3.5x y = -3.5(-6) y = ???

  9. lyzzy7
    • 3 years ago
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    21.

  10. lyzzy7
    • 3 years ago
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    thank yoouuu!:))

  11. jim_thompson5910
    • 3 years ago
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    nailed it

  12. lyzzy7
    • 3 years ago
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    can you walk me through this one too? Suppose y varies directly with x, and y = 25 when x = 140. What is the value of x when y = 36?

  13. jim_thompson5910
    • 3 years ago
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    y varies directly with x means what

  14. lyzzy7
    • 3 years ago
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    y=kx

  15. jim_thompson5910
    • 3 years ago
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    good

  16. jim_thompson5910
    • 3 years ago
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    we're given x = 140 and y = 25 so y = kx becomes 25 = k*140

  17. jim_thompson5910
    • 3 years ago
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    so k = ____

  18. lyzzy7
    • 3 years ago
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    .18

  19. jim_thompson5910
    • 3 years ago
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    I would use more decimal places for k. I'm going to use k = 0.17857 so y = kx becomes y = 0.17857x Now plug in y = 36 and solve for x y = 0.17857x 36 = 0.17857x 36/ 0.17857 = x 201.601613 = x x = 201.601613 now round to the nearest tenth to get 201.6 this is the same as 201 and 3/5 or the improper fraction 1008/5

  20. jim_thompson5910
    • 3 years ago
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    optionally... y = kx 25 = k*140 25/140 = k k = 25/140 k = 5/28 -------------------- y = kx y = (5/28)x 36 = (5/28)*x 36*28 = 5x 1008 = 5x 5x = 1008 x = 1008/5 So x = 1008/5 which is x = 201.6 in decimal form

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